Để biểu thức có nghĩa:
`<=>` \(\left\{ \begin{array}{l}x² - 1 ≥ 0\\x² + x > 0\end{array} \right.\)
`<=>` \(\left\{ \begin{array}{l}x² ≥ 1\\x(x + 1) \ne 0\end{array} \right.\)
Xét `x² ≥ 1`
`<=>` \(\left[ \begin{array}{l}x ≥ 1\\x ≤ -1\end{array} \right.\)
Xét `x(x + 1) > 0`
`<=>` \(\left\{ \begin{array}{l}x \ne 0\\x + 1 \ne 0\end{array} \right.\)
`<=>` \(\left\{ \begin{array}{l}x \ne 0\\x \ne -1\end{array} \right.\)
Vậy
\(\left\{ \begin{array}{l}x \ne 0\\x ≥ 1\\ x < -1\end{array} \right.\)
